The overall objective of this study is to investigate the normal supraspinatus tendon insertion site in the shoulder as well as its ability to heal back to its bony insertion under a range of controlled mechanical environments in an in vivo animal model. Little knowledge currently exists on the natural repair process of the insertion site after surgical repair, and as a result, little can be done to improve the tissue's ability to heal. Clinically, while the role of the post operative activity protocol is not well understood, it is believed to greatly influence the healing tissue. In order to accurately control the activity level and to quantitatively assess the healing tissue following repair, an animal model is necessary. Reliable and controlled information from the healing response in the animal model will not only provide basic information on the mechanistic nature of this healing process, but might also begin to provide insight regarding an appropriate post-operative rehabilitation protocol following, for example, a rotator cuff repair. Biomechanical, biologic, and histologic techniques established in our laboratories will allow for a rigorous and quantitative assessment of the healing tissue and the mechanisms of its response. Tendon insertions to bone will be surgically injured and repaired and subjected to various post operative activity levels. Our global hypothesis is that in vivo mechanical factors (exercise vs. cage activity vs. immobilization) will cause a change in the mechanical properties, composition, and organization of the healing insertion site.